The invention relates to tool handle trigger switch circuits for applying voltage from an AC source to a portable tool electric motor.
Soft turn-on circuitry using a current limiting resistor for limiting the amount of power initially applied to a load from a power source is known in the prior art. This is typically accomplished by a current limiting resistor. This type of soft turn-on circuitry has not been applied to tool handle trigger switches because of the heat generated by the current limiting resistor and the inability to dissipate same within the small confines of a compact tool handle trigger switch. Instead, soft start tool handle trigger switch circuitry uses an SCR and gradually phases-on the SCR to provide soft turn-on. Initially, the SCR is on for only a small portion of the AC cycle, which portion is increased with subsequent cycles to gradually apply power to the portable tool electric motor. This phasing-on soft start circuitry is objectionable because of its high cost, including the SCR, and concerns about reliability.
The present invention provides a soft start tool handle trigger switch circuit for applying voltage from an AC source to a portable tool electric motor without the expense of the above noted phasing-on circuitry. The present invention uses a current limiter connected in series between the AC source and the motor, and solves the above noted heating problem.